Method of drilling and drill bit therefor



United States Patent 72] Inventors l-lorst H. l-lasiba Pittsburgh; Joseph H. Messmer, Ollara Township, Allegheny County, Pennsylvania [211 App]. No. 763,132 [22] Filed Sept. 27, 1968 [45] Patented Nov. 24, 1970 [73] Assignee Gull Research & Development Company Pittsburgh, Pennsylvania a corporation of Delaware [54] METHOD OF DRILLING AND DRILL BIT THEREFOR 13 Claims, 4 Drawing Figs.

[52] US. Cl. 175/67, 175/410, 175/422 [51] 1nt.Cl E2lb 7/l8,- E21c 13/00 [50] Field of Search 175/67, 410, 422

[5 6] References Cited UNITED STATES PATENTS 3,384,192 5/1968 Goodwin et al 175/67 3,402,780 9/1968 Goodwinetal 3,417,829 12/1968 Achesonetal.

ABSTRACT: A drilling method and drill bit for-the hydraulic jet drilling of wells. in the drilling method a plurality of grooves separated by intervening ridges is cut in the bottom of the borehole of a well by high-velocity streams of abrasiveladen liquid and downwardly tapering rounded loading elements are inserted into the grooves. On the application of downward force the ridges arebroken by the lateral surfaces of the loading elements exerting a force in a radial direction that eccentrically loads the ridges to place rock in the ridges under tension. The downwardly tapering loading elements are positioned to ride in grooves cut in the bottom of the borehole by high-velocity streams of abrasive-laden drilling liquid discharged from nozzles in the bit. The maximum radial dimension of the loading elements is larger than the width of the grooves.

METI OD or DRILLING AND DRILL BIT THEREFOR This invention relates to thedrilling of wells by hydraulic jet drilling and more particularly to a method and drill bit for use in hydraulic jet drilling of hard formations.

In the usual rotary drilling method, a bit connected to the lower end of a drill string is rotated against the bottom of the borehole of the well while a heavy weight is applied to the bit by drill collars forming the lower end of the drill string. A drillingrnud is circulated down the drill stringthrough outlets in the drill bit and upwardly around'the drill string to carry cuttings from the well. Most of the bits used in rotary drilling operations are rock bits in which a cone-shaped roller having teeth along its outer surface engages the bottom of the borehole to crush the rock and thereby break rock particles from the formation. Drill bits that have been successfully used in drilling soft formations are frequently referred to as drag or fish tail" bits. They? have stationary downwardly directed sharp cutting elements that cut into the bottom of the borehole. Fish tall bits are not effective in drilling hard formations because of inability of cutting elements to penetrate the bottom without excessive bit load and torque and rapid wear of the cutting elements. I

One type of bit that has been used withincreasing frequency in rotarydrilling' operations is referred to as the jet bit. The conventional jet bits are provided with nozzles which direct a stream of drilling mud downwardly against the bottom of the formation with the primary'purpose of sweeping cuttings from the bottom of thehole to prevent regrinding of the cuttings. In soft formations, the stream of drilling mud discharged from jet bits may penetrate the formation being drilled and thereby increase the rate of drilling of soft formations, but the conventional jet bits have not been effective in increasing drilling rates in hard formations. Higher drilling mud velocities have improved the drilling rate of drag bits in soft formations by removing cuttings, but have not made drag bits effective in hard formations because the cutters still fail to penetrate the rock. Hard formations are, in general, formations having a compressive strength of 20,000 p.s.i. or higher.

Drill bits having tungsten carbide inserts in the outer surface of the rollers have been used to increase the drilling rate in hard formations. Such bits are able to withstand the severe abrasion caused by hard formations much better than the ordinary roller bit. However, the rate of drilling of hard formations even with bits having tungsten carbide inserts in their outer surface is slow. Moreover, the bearings of such bits frequently fail before the tungsten carbide inserts, at least partly because of the heavyweight placed on the bit. The heavy weight applied to the drill bit necessitates heavy-walled drill pipe to transmit the torque required to rotate the bit.

In a drilling method, designated hydraulic jet drilling, that has recently been developed to increase the rate of penetration of hard formations, an abrasive-laden liquid, as distinguished from a drilling mud, is pumped down the drill string and discharged from nozzles in a drill bit at an extremely high velocity of at least 500 feet per second, and preferably higher than 650 feet per second, against the bottom of the borehole.

The drill bit is rotated to cause the high-velocity streams discharged from the nozzles to travel over the bottom of the borehole and penetrate the formation being drilled. The drill bit rides on the top of any ridges in the bottom of the borehole and breaks the ridges to thereby lower the drill bit and cause deeper penetration of the formation by the high-velocity streams of abrasive-laden liquid. a

This invention resides in a methodand drill bit for use in the hydraulic jet drilling process. In themethod, a plurality of concentric grooves and a central hole are cut by extremely highvelocity streams in a manner to leave intervening unsupported v ridges. Loading elements that taper downwardly in cross section along a radius of the bit are inserted into the grooves to apply a force having a substantial componentin the radial direction to the ridges to break the ridges. The drill bit has a cylindrical body closed at its lower end by a bottom member. The upper end of the drill bit body is adapted tobeconnected to the lower end of astring of drill pipe for delivery of drilling liquid into the drill bit. A plurality of nozzles extend downwardly through the bottom member -of the drill bit in position to cut from the bottom of the borehole a central hole and a plurality of concentric grooves. Nozzles located in the drill bit farthest from the center of rotation of the drill bit slope outwardly and downwardly to cut the borehole to the desired gauge. Abrasion-resistant loading elements extend downwardly'from the bottom of the drill bit in position to ride in the grooves cut by the high-velocity stream. The loading elements arelarger at the level of the lower surface of the bottom member of the bit than the width of the grooves and decrease in size downwardly. Weight applied to the drill bit causes the lower end of the loading elements to enter the grooves and the elements to apply a downward and radial force to the ridges to break the ridges and lower the bit. In a preferred form of this invention, the elements are hemispheres having flat planar surfaces oriented such that a horizontal line in the planar surface is perpendicular to a line from the load ing element to the center of rotation of the drill bit.

In the drawings:

FIG. 1 is a diagrammatic elevational view of a drilling rig employing the drill bit of this invention with associated equipment for the drilling of a well.

FIG. 2 is a longitudinal sectional view taken along section line II-II in FIG. 3 of the drill bit of this invention.

FIG. 3 is a plan view looking upwardly at the bottom of the drill bit illustrated in FIG. 2.

FIG. 4 is a vertical sectional view along section line IV-IV in FIG. 3 showing the bottom of the borehole.

Referring to FIG. 1 of the drawings, a drilling rig indicated generally by reference numeral 10 is illustrated in place over a well 12 having casing 14 set in its upper end. The borehole of the well extends downwardly beyond the lower end of casing 14 to a total depth 16. A drill string 18, which ordinarily includes drill pipe connected to the lower end of a kelly 20 and drill collars connected to the lower end of the drill pipe, is suspended from a swivel 22 supported by drilling rig 10. The drill bit of this invention, indicated generally by reference nu metal 24, is secured to the lower end of drill string 18.

Drill string 18 is rotated in the borehole by a rotary table 26 driven by a shaft 28 connected to a power source, not shown. A conduit 30 extends from the upper end of the well to apparatus 32 identified by the legend Drilling Liquid Treatment. The apparatus 32 generally consists in a screen to remove oversize cuttings, separators to remove broken particles smaller than the abrasive used in the drilling operation, and a cooler for reducing the temperature of the recirculated abrasive-laden drilling liquid. Apparatus32 also includes hoppers or other means for introducing fresh abrasive particles into the drilling liquid to replace particles of abrasive broken into fines and removed from the drilling liquid and to supply additional abrasive for the increased volume of drilling liquid required as the hole becomes deeper. A line 34 connects the apparatus 32 to high-pressure pumps 36 which pump the drilling liquid through pipe 38 into the upper end of swivel 22 for delivery into kelly 20.

Referring to FIG. 2, the drill bit 24 has a hollow cylindrical body 40 with a centralopening 42 of enlarged diameter closed at its lower end by a bottom member 44. Extending upwardly from the body 40 is a threaded shank 46 for connection to the lower end of the drill string 18. A throat 48 extends from the upper end of the shank 46 downwardly into opening 42 for the delivery of drilling liquid from the drill string into the central opening 42 within the drill bit body 40.

Secured to the lower surface of bottom member 44 is a backsplash plate 50 of an abrasion-resistant material such as a tungsten carbide alloy. Backsplash plate 50 may be secured to bottom member 44 by any suitablemeans such as silver solder or bolts. A plurality of nozzles, referred to generally as nozzles 52, extend downwardly through the bottom member 44 and backsplash plate 50. The nozzles 52 are constructed of an abrasion-resistant material such as tungsten carbide and may be cemented in place in openings through the bottom member and backsplash plate with an epoxy resin or held in place by mechanical means.

A number of different series of nozzles 52 are provided to cut the desired pattern of grooves and holes on the bottom of the borehole. It is essential to this invention that the nozzles be positioned to cut a central hole, an annular groove having an outer diameter equal to the borehole diameter, and intervening annular grooves separated by ridges having a width permitting the ridges to be easily broken. Ridges having a maximum thickness of three-fourths inch or less usually can be broken easily and rapidly with a low weight, e.g., less than 1200 pounds per inch of diameter, on the bit. All of the ridges will be unsupported, i.e., the outer ridge is spaced from the borehole wall and there is no central core to support the innermost ridge. The number of series of nozzles will depend on the bit diameter.

Spacing and location of the nozzles in the bit are selected to cut grooves of substantially equal depth separated by ridges that can be readily broken. Because of the longer distances traveled by the nozzles of greatest distance from the center of rotation as the bit is rotated, the number of nozzles in a series of nozzles should be larger than in a series located nearer the center of rotation. There should be at least two nozzles in each series so that if one nozzle in the series becomes plugged, there will be at least one nozzle remaining in operation.

Referring to FIG. 3, a pair of inwardly slanting nozzles 52a is located near the center of rotation 54 of the drill bit. Located at the same distance from the center of rotation of the drill bit 24 illustrated in FIG. 3 is a pair of vertical nozzles 52b. The inwardly slanting nozzles 52a are at an angle whereby the high-velocity streams discharged from them cut a central hole 56 in the bottom of the borehole as the drill bit is rotated. The high-velocity streams discharged from vertical nozzles 52!: cut a groove 58 separated from the central hole 56 by a ridge 60.

Next farthest from the center of rotation 54 are vertical nozzles 520 which are positioned at a large enough distance from the center of rotation to cut a groove 62 concentric to groove 58 and separated from groove 58 by a ridge 64. Another series of vertical nozzles 52d is spaced still farther from the center of rotation to cut a groove 66 separated from groove 62 by ridge 68.

Next farthest from the center of rotation are nozzles 52e which slant outwardly at a slight angle from the vertical to cut a groove 72 having an outwardly sloping inner wall. The final series of nozzles 52fis placed around the perimeter of the drill bit and slants outwardly at an angle from the vertical larger than the angle of nozzles 52e to cause the jet stream discharged from nozzles 52fto impinge against the bottom of the borehole and cut a groove 74 having an outer diameter slightly larger than the maximum diameter of the drill bit to prevent binding of the drill bit against the borehole wall as the drill bit is rotated. Grooves 72 and 74 are separated by a ridge 73.

A plurality of elements adapted to apply a compressive load having a substantial component extends downwardly from the lower surface of the backsplash plate 50. Those elements are hereinafter called loading elements 76. The loading elements 76 are positioned at a distance from the center of rotation that will cause the loading elements 76 to ride in the grooves cut in the bottom of the borehole by the high-velocity streams discharged from nozzles 52. ln the preferred form of the invention and as best illustrated in FIG. 2, the loading elements are hemispherical and have oppositely facing flat planar surfaces 78 located to bear against the ridges separating the grooves. Surfaces 78 are oriented so that a horizontal line in the planar surface is perpendicular to the radius of the drill bit passing through the center of the loading elements. The essential shape of the loading elements 76 is that they be narrow enough at their lowest point to enter the grooves and increase in width to a width, at their base substantially in the plane of the lower surface of the bottom member, exceeding the width of the groove in which the loading element travels. The increase in width should be rapid enough to preclude the lower end of the loading elements engaging the bottom of the borehole. For example, if extended to intersect, planar surfaces 78 should meet at an angle of at least 60. The loading elements 76 also serve to maintain a desired minimum stand off between the nozzle outlets and the bottom of the grooves. For this reason the loading elements should extend downwardly from the lower surface of the bottom member 6 inch to 1% inches.

The weight applied to the drill bit is transferred to the ridges, as is best shown in FIG. 4, by the loading elements. Loading elements 76c is -shown engaging ridges 72 and 73. Loading element 76a is shown engaging ridges 64 and 68. The loading elements exert against the ridges a forcehaving a radial component that has a substantial bending moment about the bases of the ridges causing the rock to fail in tension.

Loading elements of other shapes than that shown in the drawings can be used. For example, the loading elements may be hemispherical without the planar surfaces 78. Planar surfaces 78 are advantageous in increasing the area of the standoff elements that bear against the ridges and increasing the component of force in a radial direction exerted against the ridges. Conical stand-off elements can be used. Wedge-shaped elements of substantially rectangular horizontal cross section also can be used, but their length in a circumferential direction should not be long and their leading edges should be dull or rounded. It is important to this invention that the loading elements exert a load tending to bend the ridges in a radial direction rather than a cutting action by their leading edge. Wedge-shaped loading elements of arcuate horizontal cross section with a radius of curvature substantially equal to the radius of the groove in which it travels can also be used. Because of the arcuate shape, such loading elements can be of substantial length without causing the leading edge to dig into or cut the ridges. Loading elements 76 may be integral with the backsplash plate or secured to the backsplash plate by suitable means such as silver solder. The loading elements are made of a hard, abrasion-resistant material. The term abrasion-resistant material is used to designate material, such as tungsten carbide alloys, that are harder than steel.

The loading elements 76a nearest the center of rotation of the drill bit are positioned to ride in groove 62 cut by nozzles 520. Since nozzles 52c are vertical, loading elements 76d are the same distance from the center of rotation as nozzles 52c. Loading elements 76b are positioned at a greater distance than loading elements 76a from the center of rotation of the drill bit and are adapted to ride in the grooves 66 and bear against ridges 68 and 72. The outermost loading elements 76c ride in groove 70 and bear against ridges 72 and 73. Because nozzles 52e slant outwardly at a slight angle, the loading elements 76c are at a slightly larger distance from the center of rotation of the drill bit than nozzles 52e to center the loading elements in groove 70.

It is essential for fast drilling of hard formations having a compressive strength exceeding 20,000 p.s.i. for which this invention is most useful, that an abrasive be suspended in the drilling liquids. Clear liquids or drilling muds containing the usual suspended solids give very slow drilling rates in hard rock formations even at jet velocities exceeding 650 feet per second. The size of the abrasive particles used in the jet drilling method is such that the abrasive can be handled without difficulty in the high-pressure pumps. Ferrous abrasive particles having a size in the range of 10 to 80 mesh in the US. Sieve Series have been found to be suitable. Abrasive concentrations of 1 to 20 percent by volume can be used. An abrasive concentration in the range of 2 to 10 percent by volume is preferred. Nozzles having a diameter in the range of three thirty-seconds inch to three-sixteenths inch are preferred when using 10 to 80 mesh abrasive particles. Larger nozzles require excessive capacity of high-pressure pumps 36 to obtain the required high jet velocity.

The width of grooves cut by nozzles having a diameter in the range of three thirty-seconds to three-sixteenths inch is approximately one-eighth inch larger than the nozzle diameter. It is desirable'to locatethe nozzles to'leave ridgesnot more than three-fourths inch wide between the grooves. To apply the desired forces in a radial direction to the ridges, the load ing elements should have a maximum radial dimension substantially larger than the width of the grooves cut in the bottom of the borehole, For example, loading elements having a base diameter of one inch, and an angle between the planar surfaces of approximately 90, are suitable in a drill bit in which the nozzles have a diameter of one-eighth inch.

In the operation of the drill bit of this invention, the drill bit is rotated in the borehole by rotary table 26. A drilling liquid containing an abrasive, preferablycontaining 2 to percent of ferrous abrasive particles having a size in the range of 10 to 80 mesh, is pumped through pipe 38 into the upper end of kelly 20 and down the drill string 18 to the drill bit 24. Drill string 18 ordinarily includes drill collars, as necessary, to apply a weight to the bit not'exceeding l200 pounds per inch of bit diameter. The drilling liquid is discharged through the nozzles at a velocity of at least 500 feet per second, preferably in the range of 650 to 900 feet per second, against the bottom .of the borehole. A pressure drop of at least about 4000 p.s.i. is maintained through the nozzles. Cuttings from the bottom of the borehole, abrasive particles, and the-drilling liquid circulate up the borehole around the drill string, and are discharged through conduit 30 into apparatus 32 for treatment of the drilling liquid.

Referring to FIGS. 3 and 4, the drilling liquid discharged from nozzles 52a slants inwardly and cuts the central hole 56 in the bottom of the borehole. The high-velocity jet streams from nozzles 52b cut a groove 58 surrounding the central hole 56. Because the jet streams discharged from nozzles 52a and 52b have some width and the nozzles are at the same distance from the center of rotationpf the drill bit, the jet streams overlap and cut the topfrorn the ridge60 separatingcentral hole 56 and groove 58, therebyeliminating the necessity of any stand-off elements positioned to travel in groove 58.

The high-velocity streams of drilling liquiddischarged from nozzles 52 cut a series of conc'entricgrooves in the bottom of the borehole separated by intervening ridges. The-stand-off elements 76 ride in the grooves andbear against the faces 'adjacent the groove of the ridges on both sides of the groove. For example, the inner tapered surface of the stand-off element 76a exerts a radial force on the ridge 64 that places the surface of the ridge farthest from the center of rotation in tension. The outer surface of the stand-off element 76a engages the ridge 68 and places the inner surface of that ridge in tension. Thus, there is eccentric loading of the ridges. Weaknessof rock in tension. causes the rock tobreak even though the weight applied to the bit,is small. Continued rotation of: the drill bit results in continued breaking of the ridges, lowering of the drill bit, and deepening of the gr ooves.

The drill bit of this invention allows rapid drilling of hard formations that cannot be effectively drilled bygbits having mechanical cutting elements designed to cut into the rock. By applying a load against the ridges in a radial direction, a bending moment is created in adirection such that it is opposed by the narrowest dimension of the ridgeswith the result that a low bit weight will break the ridges. Because thereis neither a central core nor rock supported by the borehole wall, all rock mechanically broken by the bit, as distinguished from rock eroded by the abrasive in the high-velocity jet streams, is exposed to a bending moment.The low bit .weight required to break the rock greatly reduces the torque required to rotate the drill bit and results in rapid drilling of hard rock formations that cannot becut by the cutting elements in drag bits. Moreover, because theloading elements travel in grooves in the bottom of the borehole, they increase the stability and smoothness of operation of the drill bit.

We claim:

1. A method of drilling a borehole in hard formations comprising rotating a drill bit at .the bottom of the borehole; discharging an abrasive-laden slurry at a velocity of at least 500 feet per second downwardly from the drill bit in a plurality'of hydraulic jet streams at substantially the same elevation in the drill bit and positioned to cut an outer groove having an outer diameter equal to the diameter of the borehole, a central hole, and a plurality of concentric intervening grooves separated by intervening ridges; inserting downwardly into grooves in the bottom of the borehole spaced downwardly tapering loading elements extending downwardly from the lower end of the drill bit; and applying a downward load to the drill bit to force lateral surfaces of the loading elements into engagement with the ridges between the grooves to break the ridges and allow lowering of the drill bit in the borehole.

2. A method as set forth in claim 1 in which the velocity of the abrasive-laden jet streams is at least 650 feet per second, the abrasive is a ferrous abrasive in a concentration in the drilling liquid in the range of 2 to 10 percent by volume, and a force not exceeding 1200 pounds per inch of diameter of the borehole is applied to the drill bit to break the ridges.

3. A drill bit for the drilling of boreholes in hard formations comprising a drill bit body having a central opening closed by a bottom member; a backsplash plate of abrasion-resistant material on the lower surface of the bottom member; nozzles extending downwardly through the bottom member and backsplash plate for discharging high-velocity jet streams of abrasive-laden liquid; said nozzles being positioned to discharge jet streams cutting in the bottom of the borehole a central hole, an outer annular groove having an outer diameter equal to the outer diameter of the borehole and intermediate grooves separated by intervening ridges; and downwardly tapering loading elements of abrasion-resistant material mounted in and extending downwardly from the backsplash plate and positioned to ride in the grooves; said loading elements having a maximum dimension at their upper end in a direction along a radius of the bit wider than the grooves whereby the loading elements apply a load in a radial direction to the ridges.

4. A drill bit as set forth in claim 3 in which the nozzles have a diameter in the range of three thirty-seconds to three-sixteenths inch.

5. A drill bit as set forth in claim 3 in which the loading elements are positioned to travel in each of the grooves other than the outer groove.

6. A drill bit as set forth in claim 3 in which the nozzles positioned nearest the center of rotation of the drill bit slant downwardly and inwardly, the nozzles positioned at the largest distance from the center of rotation of the drill bit slant downwardly and outwardly, and the loading elements are positioned to cause each ridge substantially uncut by a jet stream to be engaged by a loading element.

' 7. A drillbit as set forth in claim 3 in which nozzles slope downwardly and inwardly to cut the central hole, other nozzles slope downwardly and outwardly to cut an outer groove having an outer diameter equal to the outer diameter of the borehole, still other nozzles are positioned to cut intermediate grooves cut by intervening ridges, and downwardly tapering loading elements extend downwardly from the backsplash plate in a position to ride in each of the grooves other than the outermost and innermost groove.

8. A drill bit as set forth in claim 3 in which the loading elements are hemispherical.

9. A drill bit as set forth in claim3 in which the loading elements are hemispherical and have substantially flat planar surfaces facing in a radial direction.

10. A .drill bit as set forth in claim 3 in which a cross section of the loading elements taken along a radius of the drill bit tapers downwardly.

11. A drill bit as set forth in claim 3 in which the loading elements extend downwardly for a distance of wt inch to 1 /2 inches below the backsplash plate and taper at an angle such that the loading elements engage the ridges in the bottom of the borehole and thereby maintain the lower end of the loading elements above the bottom of the grooves.

12. A drill bit as set forth in claim 3 in which the surfaces of the loading elements that engage the ridges on opposite sides of a groove are at an angle of at least 60 with one another. 

